200 BULLETIN UNITED STATES GEOLOGICAL SURVEY. \Yol.Y. 



fossils of the former been foimcl in tlie latter, and yet botli have been 

 considered conformable to the Fox Hills Cretaceons. If they represent 

 different portions of the group, localities may yet be discovered in which 

 the two will be in superposition. This, of course, is for the present a 

 mere speculation, yet it seems to me that the facts point to the indica- 

 tion that these two localities represent two portions of the grouj) sepa- 

 rated by a period of orographic disturbance. 



CONCLUSION. 



In conclusion, I briefly recapitulate the points indicated by the facts 

 observed in Western Wyoming and Southeastern Idaho. 



1. During the period represented by the deposition of the Laramie 

 Group as observed in the district, there was a progressive subsidence 

 followed at the close by a general elevation, which perhaps foreshadowed 

 the disturbance which was to take place after the complete deposition of 

 the beds. 



2. The fossils of the group thus described are equivalent to those of 

 the Bear River Estuary Beds, which Dr. White is inclined to think are 

 older in their facies than those of more eastern localities. 



3. Intense orographical disturbance took place at the end of the 

 deposition of the beds comi^rising the group in these localities, which 

 resulted in the ui>heaval of the area Avest of Green Eiver Basin to beyond 

 the limits of our district, accompanied by great folding and faulting in 

 the strata of the district. 



4. It is probable that this disturbance took place before the close of 

 the Post-Cretaceous period, and resulted in the separation of the Lara- 

 mie Group into at least two portions, an eastern and a western part. 



5. There was a period of vast erosion which began in the time imme- 

 diately following the uplift, and has continued to the present time. 



G. Following the disturbance, there was a progressive subsidence by 

 which the western limits of the eastern or newer Laramie beds were over- 

 lapped, and which continued until the Upper Wahsatch fresh-water 

 beds were deposited unconformably on the upturned and denuded edges 

 of Silurian, Carboniferous, Jura-Trias, and Cretaceous, as well as the 

 older Laramie strata. 



